1. Field of the Invention
The present invention relates to a device and a method for reinforcing an optical fiber fusion spliced part which covers the optical fiber fusion spliced part with a sleeve-like protective member having a reinforcing rod and reinforces the optical fiber fusion spliced part by shrinking generated by heating.
2. Description of the Related Art
In the related art, in the fusion splicing of the optical fibers, the fusion splicing is performed by removing fiber coating portions of connecting ends and melting abutting end portions of exposed glass fiber portion by heating. The glass fiber portions which are connected by fusion splicing exhibit a weak mechanical strength and hence, the glass fiber portions are reinforced with a protective member. The protective member is usually constituted by accommodating a heat fusing tube made of a heat-fusing adhesive resin together with a reinforcing rod in the inside of a heat shrinking tube which shrinks in the radial direction by heating (see Japanese Unexamined Patent Publication Hei11(1999)-52163 and Japanese Unexamined Patent Publication Hei09(1997)-21926, for example).
FIG. 4A and FIG. 4B are views showing a related-art method for reinforcing a fusion spliced part, wherein FIG. 4A is a view showing an example which reinforces a fusion spliced part of a single optical fiber and FIG. 4B is a view showing an example which reinforces a fusion spliced part of an optical fiber ribbon. In the drawing, symbols 1, 1′ indicate optical fibers, symbol 2 indicates glass fiber portions, symbol 3 indicate fiber coating portions, symbol 4 indicates a fusion spliced part, symbol 5 indicates a protective member, symbol 6 indicates a heat shrinking tube, symbol 7 indicates a heat fusing tube, symbol 8 indicates a reinforcing rod, symbol 9 indicates a heating platform, symbol 10 indicates a heater, and symbol 11 indicates a heating mechanism.
In the example shown in FIG. 4A which depicts the single optical fibers, the glass fiber portions 2 of the optical fibers 1 is exposed by removing the fiber coating portions 3 at the connecting ends and the fusion splicing is performed by making distal ends thereof abut to each other and connecting them by an arc discharge. The protective member 5 has a length which can cover given ranges of fiber coating portions 3 at both sides of the glass fiber portions 2. The protective member 5 is configured to accommodate the heat fusing tube 7 made of a hot-melt adhesive resin and the reinforcing rod 8 made of stainless steel, glass, ceramics or the like in the inside of the heat shrinking tube 6. The optical fibers 1 which are connected by fusion are inserted into the inside of the heat fusing tube 7 such that the fusion spliced part 4 is positioned as the center of the heat fusing tube 7 and is heated by the heating mechanism 11. The heating mechanism 11 comprises he heating platform 9, the heater 10 and the like. Due to this heating, the heat fusing tube 7 is softened and fused and, at the same time, the heat shrinking tube 6 is shrunken and decreases a diameter thereof in the inner radial direction.
By shrinking the heat shrinking tube 6 and narrowing of the diameter of the heat shrinking tube 6, the heat fusing tube 7 which is fused by heating covers peripheries of the glass fiber portions 2 together with the reinforcing rod 8 such that the heat fusing tube 7 which is fused by melting embeds a space portion in the inside of the heat shrinking tube 6. When the heat shrinking tube 6 and the fused heat fusing tube 7 are cured, the fusion spliced part 4 is protected and is reinforced in a given range including a portion of the fiber coating portions at both sides of the glass fiber portions 2.
Also with respect to an example of the optical fiber ribbon shown in FIG. 4B, in the same manner as the single optical fibers 1, the optical fibers 1 are configured such that the fiber coating portions 3 of the connecting ends are removed to expose glass fiber portions 2 and distal ends of the glass fiber portions 2 are made to abut each other and are collectively connected by fusion splicing using arc discharging or the like. The protective member 5 has a length which allows the protective member 5 to cover given ranges of the fiber coating portions 3 at both sides of the glass fiber portions 2. That is, the protective member 5 is configured such that the heat fusing tube 7 of a hot melt adhesive resin and the reinforcing rod 8 are housed in the inside of the heat shrinking tube 6 having a diameter larger than the heat shrinking tube 6 of the single optical fiber 1.
The heat fusing tube 7, for example, is formed into an elliptical shape and has a shape and a size which allow the heat fusing tube 7 to house a large number of optical fibers arranged in parallel in a row, while the reinforcing rod 8 is also formed such that the reinforcing rod 8 has a semicircular shape and has a diameter which allows the optical fibers to be arranged in a row on a flat surface thereof. Then, in the same manner as the constitution shown in FIG. 4A, the optical fibers 1′ which are to be connected by fusion splicing are inserted into the inside of the heat fusing tube 7 such that the fusion spliced part 4 is positioned at the center of the heat fusing tube 7. These components are heated by the heating mechanism 11 which comprises the heating platform 9, the heating heater 10 and the like. Due to such heating, the heat fusing tube 7 can be softened and fused and, at the same time, the heat shrinking tube 6 can be shrunken and the diameter of the heat shrinking tube 6 can be narrowed in the inner radial direction.
With respect to the above-mentioned reinforcement of the fusion spliced part, the above-mentioned Japanese Unexamined Patent Publication Hei11(1999)-52163 discloses the technique in which the generation of a bending force on the optical fibers at the time of heat shrinking can be eliminated by exposing the reinforcing rod 8 from both ends of the heat shrinking tube 6. Further, Japanese Unexamined Patent Publication Hei09(1997)-21926 discloses the technique in which in view of a fact that at the time of protecting the fusion slicing portion with the protective member 5, when the fusion spliced part is protected and fixed in a state that the optical fibers are bent, this becomes a cause of the increase of transmission loss and hence, the protective member 5 is heated while adding a fixed tension to the optical fibers 1.
When the protective member 5 which covers the fusion spliced part 4 of the optical fiber is placed on and is heated by the heating platform 9 of the heating mechanism 11, as also indicated in Japanese Unexamined Patent Publication Hei09(1997)-21926, it is necessary to fix by clamping the optical fibers 1 which are exposed from both sides of the protective member 5 using the optical fiber clamping mechanisms such that they are not moved. In this case, a support height of the optical fibers 1 is set substantially equal to a support height of the fusion spliced part. For example, with respect to the protective member 5 which is used in the single optical fiber shown in FIG. 4A, the protective member 5 is supported such that the optical fibers 1 are supported on the heated heating platform 9 substantially linearly and a support height thereof is set to D1.
However, in the fusion splicing of the optical fibers, versatile connection modes ranging from a single optical fiber mode to an optical fiber ribbon mode are adopted and, at the same time, with respect to the collective fusion splicing of the optical fibers, the collective splicing in a wide range from 2 fibers to 16 fibers or 24 fibers has been put into practice. When the number of the optical fibers is increased, a size of the reinforcing rod 8 is increased and hence, an outer diameter of the protective member 5 is also increased. Accordingly, with respect to the protective member 5 which is used in the optical fiber ribbon shown in FIG. 4B, the support height of the optical fibers 1′from the heating platform 9 assumes D2 which is higher than the support height D1 shown in FIG. 4A. On the other hand, with respect to the optical fiber clamping mechanisms which clamp and fix the optical fiber 1′, usually, the height position of the optical fiber clamping mechanisms with respect to the heating platform 9 is fixed. In both of Japanese Unexamined Patent Publication Hei11(1999)-52163 and Japanese Unexamined Patent Publication Hei09(1997)-21926, no consideration has been made with respect to such difference in the support height.
FIGS. 5A and 5B are views showing an operational state of the device of reinforcing the optical fiber fusion spliced part. In the drawing, symbol 11 indicates a heating mechanism, symbol 12 indicates optical fiber clamping mechanisms and Y indicates a void. When the protective member 5 becomes large (is increased in size) due to the reinforcement of the fusion spliced part of the optical fiber ribbon 1′, the support height of the fusion spliced part of the optical fibers is set larger than the support height of the optical fibers due to the optical fiber clamping mechanisms 12 at both sides and hence, the optical fiber 1′ is held in an upwardly projected state as shown in FIG. 5A. Accordingly, a portion of the optical fiber which is surrounded by a circle in FIG. 5A assumes a curved state.
When the protective member 5 is heated in such a state, as indicated in an enlarged manner in FIG. 5B, the heat shrinking tube 6 is shrunken in the radial direction and, when the heat fusing tube 7 is fused, the optical fiber ribbon 1′ functions so as to impede the discharge of the inside air at both end portions of the reinforcing rod 8 and hence, there exists a possibility that the air remains in the inside of the fused resin as the void Y. The void Y which is left in the inside of the protective member 5 repeats expansion and shrinking due to the change of an outside temperature and this may impart the intermittent change of stress to the optical fibers thus leading to the disconnection. Further, the expansion of the void Y imparts a side pressure to the optical fiber thus lowering the transmission loss.